Page 24 - An Introduction to Microelectromechanical Systems Engineering

What Is Micromachining? 3

• “MEMS is a way of making things,” reports the Microsystems Technology
Office of the United States DARPA [1]. These “things” merge the functions
of sensing and actuation with computation and communication to locally
control physical parameters at the microscale, yet cause effects at much
grander scales.

Although a universal definition is lacking, MEMS products possess a number of
distinctive features. They are miniature embedded systems involving one or many
micromachined components or structures. They enable higher level functions,
though in and of themselves, their utility may be limited—a micromachined pres-
sure sensor in one’s hand is useless, but, under the hood, it controls the fuel-air mix-
ture of the car engine. They often integrate smaller functions together into one
package for greater utility (e.g., merging an acceleration sensor with electronic cir-
cuits for self diagnostics). They can also bring cost benefits directly through low unit
pricing or indirectly by cutting service and maintenance costs.
Although the vast majority of today’s MEMS products are better categorized as
components or subsystems, the emphasis in MEMS technology should be on the
“systems” aspect. True microsystems may still be a few years away, but their devel-
opment and evolution relies on the success of today’s components, especially as
these components are integrated together to perform functions ever increasing in
complexity. Building microsystems is an evolutionary process; we spent the last 30
years learning how to build micromachined components, and only recently we
began learning about their seamless integration into subsystems and ultimately into
complete microsystems.
One notable example is the evolution of crash sensors for airbag safety
systems. Early sensors were merely mechanical switches. They later evolved into
micromechanical sensors that directly measured acceleration. The current genera-
tion of devices integrates electronic circuitry alongside a micromechanical sensor
to provide self diagnostics and a digital output. It is anticipated that the next
generation of devices will also incorporate the entire airbag deployment circuitry
that decides whether to inflate the airbag. As the technology matures, the airbag
crash sensor may be integrated one day with micromachined yaw-rate and other
inertial sensors to form a complete microsystem responsible for passenger safety
and vehicle stability.
Examples of future microsystems are not limited to automotive applications
(see Table 1.1). Efforts to develop micromachined components for the control of
fluids are just beginning to bear fruit. These could one day lead to the integration
of micropumps with microvalves and reservoirs to build new miniature drug
delivery systems.

What Is Micromachining?

Micromachining is the set of design and fabrication tools that precisely machine and
form structures and elements at a scale well below the limits of our human percep-
tive faculties—the microscale. Micromachining is the underlying foundation of
MEMS fabrication; it is the toolbox of MEMS.